1. Field of the Invention
The present invention relates to a method and apparatus of switching the connection of electric power feeding lines from which electric power is supplied to a signal passing through an optical fiber transmission path (for example, a transmission path of a submarine cable) through a repeater. Also, the present invention relates to an electric power feeding line switching system in which communication between terminal stations (for example, land-based terminal stations) is performed through the optical fiber transmission paths connected with each other in an optical fiber transmission path branching apparatus and the repeater while electric power is supplied from the electric power feeding lines to the signal of the optical fiber transmission paths.
2. Description of Related Art
A conventional electric power feeding line switching apparatus and a conventional electric power feeding line switching system, xe2x80x9cSwitching Method and Switching Circuit for Feeder Line of Transmission Pathxe2x80x9d disclosed in Published Unexamined Japanese Patent Application No. JP1-243734 is known as an example of a conventional electric power feeding line switching method.
FIG. 11 is a constitutional view of a conventional electric power feeding line switching system in which submarine cable transmission paths and repeaters are arranged so as to supply electric power from electric power feeding lines, of which the connection is switched in a conventional electric power feeding line switching apparatus according to a conventional electric power feeding line switching method disclosed in the Application No. JP1-243734, to a signal of the submarine cable transmission paths through the repeaters.
In FIG. 11, 1 indicates a first land-based terminal station, 2 indicates a second land-based terminal station, 3 indicates a third land-based terminal station, 8 indicates a submarine branching apparatus in which a plurality of submarine cable transmission paths are connected with each other at a branching point 24, 21 indicates a first submarine cable transmission path connecting the first land-based terminal station 1 and the submarine branching apparatus 8, 22 indicates a second submarine cable transmission path connecting the second land-based terminal station 2 and the submarine branching apparatus 8, 23 indicates a third submarine cable transmission path connecting the third land-based terminal station 3 and the submarine branching apparatus 8, 11 indicates a repeater arranged on the first submarine cable transmission path 21, 12 indicates another repeater arranged on the first submarine cable transmission path 21, 13 indicates a repeater arranged on the second submarine cable transmission path 22, and 14 indicates another repeater arranged on the second submarine cable transmission path 22. Each of the submarine cable transmission paths 21, 22 and 23 is formed of an optical fiber. An optical signal, which transmits through the first submarine cable transmission path 21 and is attenuated in a long-distance transmission, is amplified in the repeaters 11 and 12. An optical signal, which transmits through the second submarine cable transmission path 22 and is attenuated in a long-distance transmission, is amplified in the repeaters 13 and 14. A length of the third submarine cable transmission path 23 is comparatively short. Therefore, an optical signal of the third submarine cable transmission path 23 is not substantially attenuated, and no repeater is arranged on the third submarine cable transmission path 23.
Also, 5 indicates a first electric power feeding line through which electric power is supplied from the first land-based terminal station 1 to the repeaters 11 and 12, 6 indicates a second electric power feeding line through which electric power is supplied from the second land-based terminal station 2 to the repeaters 13 and 14, 7 indicates a third electric power feeding line extending from the third land-based terminal station 3 to the submarine branching apparatus 8, and 8a indicates an electric power feeding line switching circuit (or a conventional electric power feeding line switching apparatus) arranged in the submarine branching apparatus 8. The electric power feeding line switching circuit 8a normally connects the first electric power feeding line 5 and the second electric power feeding line 6 and normally disconnects the third electric power feeding line 7 from the electric power feeding lines 5 and 6. Therefore, electric power is supplied to the repeaters 11 to 14 to perform the communication between the land-based terminal stations 1 and 2. Also, when a fault occurs in the electric power feeding line 5 (or 6), the electric power feeding line switching circuit 8a switches from the connection between the electric power feeding lines 5 and 6 to another connection between the electric power feeding lines 6 (or 5) and 7.
Also, 23a indicates a control signal line through which a control signal is transmitted from the third land-based terminal station 3 to the electric power feeding line switching circuit 8a to switch a connection relationship among the electric power feeding lines 5 to 7 in the electric power feeding line switching circuit 8a. The control signal line 23a is formed of an optical fiber.
An operation of the conventional electric power feeding line switching system in the above configuration is described.
Electric power is supplied to the repeaters 11 to 14 through the electric power feeding lines 5 and 6, and an optical signal is normally transmitted between the land-based terminal stations 1 and 2 through the submarine cable transmission paths 21 and 22 while amplifying the optical signal in the repeaters 11 to 14.
When a fault occurs, for example, in the first electric power feeding line 5 placed between the first land-based terminal station 1 and the submarine branching apparatus 8, a control signal is transmitted from the third land-based terminal station 3 to the submarine branching apparatus 8 through the control signal line 23a, and a switching circuit of the electric power feeding line switching circuit 8a is operated according to the control signal. The operation of the switching circuit is such that an end of the first electric power feeding line 5, in which the fault occurs, is earthed in the submarine branching apparatus 8 to disconnect the first electric power feeding line 5 from the electric power feeding lines 6 and 7, and the third electric power feeding line 7 is connected with the second electric power feeding line 6 to enable communication between the land-based terminal stations 2 and 3 through the submarine cable transmission paths 22 and 23.
Therefore, even though a fault occurs in the first electric power feeding line 5, the first electric power feeding line 5 is disconnected from the electric power feeding lines 6 and 7, and the third electric power feeding line 7 is connected with the second electric power feeding line 6. Accordingly, electric power can be supplied to the repeaters 13 and 14 through the electric power feeding line 6 connected with the electric power feeding line 7, and a communication between the land-based terminal stations 2 and 3 can be maintained.
However, in cases where a distance between the land-based terminal station 3 and the submarine branching apparatus 8 is long, because the third submarine cable transmission path 23 is lengthened, the control signal is attenuated. In this case, there is a case where the switching circuit of the electric power feeding line switching circuit 8a cannot be correctly operated according to the attenuated control signal. Therefore, there is a problem that it is required to shorten a distance between the land-based terminal station 3 and the submarine branching apparatus 8 or to additionally arrange one or more repeaters on the third submarine cable transmission path 23.
Also, in another prior art, a relay circuit is arranged between the electric power feeding lines 5 and 6 in the electric power feeding line switching circuit 8a so as to be operated according to a feeding current passing through the electric power feeding line 5 or 6. In this prior art, when the feeding current reaches a prescribed value, the relay circuit is operated, and the switching circuit of the electric power feeding line switching circuit 8a is operated according to the feeding current passing through the electric power feeding line 5 or 6 to switch from the connection between the electric power feeding lines 5 and 6 to another connection. However, in this prior art, when a fault occurs in the first electric power feeding line 5, the feeding current is dynamically changed. Therefore, the operation of the switching circuit of the electric power feeding line switching circuit 8a is performed when a large current change occurs in the relay circuit to set the electric power feeding lines 5 and 6 to a dynamic state. In this case, there is a problem that a high voltage is generated in a contacting point of the electric power feeding lines 5 and 6 placed in the switching circuit so as to generate an electric arc.
An object of the present invention is to provide, with due consideration to the drawbacks of the conventional electric power feeding line switching method, the conventional electric power feeding line switching apparatus and the conventional electric power feeding line switching system, an electric power feeding line switching method, an electric power feeding line switching apparatus and an electric power feeding line switching system in which the connection of a plurality of electric power feeding lines is switched in a static state of electric power feeding lines without limiting a distance between a terminal station and a switching point of the electric power feeding lines. Also, the object of the present invention is to provide an electric power feeding line switching method, an electric power feeding line switching apparatus and an electric power feeding line switching system in which the feeding of electric power to repeaters is easily performed when the operation of the electric power feeding line switching system is started.
The object is achieved by the provision of an electric power feeding line switching method, in which electric power is supplied from each of a plurality of electric power feeding lines to one of a plurality of repeaters with which a plurality of optical fiber transmission paths having a branching point are connected to supply electric power to an optical communication signal transmitting through the optical fiber transmission paths, comprising the steps of:
superposing a control signal on the optical communication signal which transmits through the optical fiber transmission paths; and
controlling a connection relationship among the electric power feeding lines according to the control signal superposed on the optical communication signal to switch from one connection of the electric power feeding lines to another connection of the electric power feeding lines.
In the above steps, the control signal superposed on he optical communication signal transmits through one optical fiber transmission path, and the connection relationship among the electric power feeding lines is switched according to the control signal.
Accordingly, because the feeding of electric power to the electric power feeding lines is set to a stable state, the connection of the electric power feeding lines can be switched in the stable state of the electric power feeding lines. Therefore, there is no probability that a high voltage is generated in a connecting point of the electric power feeding lines so as to generate an electric arc, and a connection change of the electric power feeding lines can be reliably performed.
Also, because the control signal transmits through one optical fiber transmission path, even though the optical fiber transmission path is long, electric power can be supplied from the electric power feeding line to the control signal of the optical fiber transmission path through the repeater connected with the optical fiber transmission path to amplify the control signal. Therefore, there is no probability that the control signal is attenuated, and the connection of the electric power feeding lines can be reliably switched according to the control signal regardless of the length of the optical fiber transmission path.
It is preferred that the step of superposing a control signal includes the step of superposing the control signal on the optical communication signal which is transmitted between terminal stations through the optical fiber transmission paths connected with the terminal stations.
Because the control signal passes through one optical fiber transmission path, an optical fiber for transmitting only the control signal is not required. Therefore, the connection of the electric power feeding lines can be reliably switched at a low cost.
It is also preferred that the electric power feeding line switching method further comprises the steps of:
transmitting a second control signal through one optical fiber transmission path, which is connected with one electric power feeding line corresponding to no fault through one repeater, in cases where a fault occurs in one of the electric power feeding lines;
earthing one end of the electric power feeding line corresponding to the fault on a side of a connection point of the electric power feeding lines according to the second control signal to disconnect the electric power feeding line corresponding to the fault from the electric power feeding lines corresponding to no fault; and
connecting the electric power feeding lines corresponding to no fault with each other at the connection point to switch from the connection of all electric power feeding lines to another connection of the electric power feeding lines corresponding to no fault.
In the above steps, even though a fault occurs in one electric power feeding line, because the connection switching of the electric power feeding lines is not performed according to a level change of the electric power feeding line but is performed according to the second control signal transmitting through one optical fiber transmission path, the connection of the electric power feeding lines can be switched in the stable state of the electric power feeding lines. Therefore, there is no probability that a high voltage is generated in a connecting point of the electric power feeding lines so as to generate an electric arc, and a connection change of the electric power feeding lines can be reliably performed.
Also, because the electric power feeding line corresponding to the fault is earthed and because the electric power feeding lines corresponding to no fault are connected with each other, communication can be reliably performed through the optical fiber transmission paths corresponding to no fault.
It is also preferred that the electric power feeding line switching method further comprises the steps of earthing one electric power feeding line on a side of a connection point of the electric power feeding lines in an initial state in which the feeding of electric power to the other electric power feeding lines is started.
Because an electrostatic capacity of a system including the electric power feeding lines, the repeaters and the optical fiber transmission paths is reduced in the initial state, the feeding of electric power to the other electric power feeding lines can be easily started.
It is also preferred that the step of controlling a connection relationship includes the step of switching the connection of the electric power feeding lines while monitoring an electric potential difference between an electric potential of the electric power feeding lines connected with each other at a connection point and a ground level.
In the above step, because the electric potential difference is monitored, the connection of the electric power feeding lines can be switched when the electric potential difference is lowered. Therefore, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
It is also preferred that the step of controlling a connection relationship comprises the steps of:
monitoring an electric potential difference between an electric potential of the electric power feeding lines connected with each other at a connection point and a ground level;
maintaining electric currents supplied to the electric power feeding lines; and
switching the connection of the electric power feeding lines when the monitored electric potential difference is minimized.
In the above steps, because the connection of the electric power feeding lines is switched when the monitored electric potential difference is minimized, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
It is also preferred that the step of controlling a connection relationship includes the step of switching the connection of the electric power feeding lines while reducing an electric current, which is supplied to a connection point of the electric power feeding lines, to a minimum current required to switch the connection of the electric power feeding lines.
In the above steps, because the connection of the electric power feeding lines is switched when the electric current supplied to a connection point of the electric power feeding lines is reduced to a minimum current, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
It is also preferred that the step of controlling a connection relationship comprises the steps of:
controlling an electric current, which is supplied to a connection point of the electric power feeding lines, to a minimum current required to switch the connection of the electric power feeding lines;
demultiplexing the control signal from the optical communication signal; and
automatically switching the connection of the electric power feeding lines according to the control signal demultiplexed from the optical communication signal after the electric current is controlled to the minimum current.
In the above steps, because the connection of the electric power feeding lines is switched after the electric current supplied to a connection point of the electric power feeding lines is controlled to a minimum current, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
The object is achieved by the provision of an electric power feeding line switching apparatus, in which a connection of a plurality of electric power feeding lines, each of which is connected with an optical fiber transmission path through a repeater to supply electric power from the electric power feeding lines to an optical communication signal of the optical fiber transmission paths through the repeaters, is switched, comprising:
optical signal receiving means for receiving the optical communication signal which includes a control signal and transmits through the optical fiber transmission paths;
control signal demultiplexing means for detecting the control signal by demultiplexing the control signal from the optical communication signal received by the optical signal receiving means; and
an electric power feeding line selector switch for controlling the connection of the electric power feeding lines according to the control signal detected by the control signal demultiplexing means by switching one connection of the electric power feeding lines to another connection of the electric power feeding lines.
In the above configuration, the switching of the connection of the electric power feeding lines is performed according to the control signal which is transmitted through one optical fiber transmission path with the optical communication signal.
Accordingly, the connection of the electric power feeding lines can be switched according to the control signal when the electric power feeding lines are electrically set to a stable state. Therefore, there is no probability that a high voltage is generated in a connecting point of the electric power feeding lines so as to generate an electric arc, and a connection change of the electric power feeding lines can be reliably performed.
Also, because the control signal transmits through one optical fiber transmission path, even though the optical fiber transmission path is long, electric power can be supplied from the electric power feeding line to the control signal of the optical fiber transmission path through the repeater connected with the optical fiber transmission path to amplify the control signal. Therefore, there is no probability that the control signal is attenuated, and the connection of the electric power feeding lines can be reliably switched according to the control signal regardless of the length of the optical fiber transmission path.
It is preferred that a second control signal, which transmits through one optical fiber transmission path connected with one electric power feeding line corresponding to no fault through one repeater, is received by the optical signal receiving means in cases where a fault occurs in one of the electric power feeding lines, one end of the electric power feeding line corresponding to the fault is earthed on a side of a connection point of the electric power feeding lines according to the second control signal by the electric power feeding line selector switch to disconnect the electric power feeding line corresponding to the fault from the electric power feeding lines corresponding to no fault, and the electric power feeding lines corresponding to no fault are connected with each other at the connection point according to the second control signal by the electric power feeding line selector switch to switch from the connection of all electric power feeding lines to another connection of the electric power feeding lines corresponding to no fault.
In the above configuration, even though a fault occurs in one electric power feeding line, because the connection switching of the electric power feeding lines is not performed according to a level change of the electric power feeding line but is performed according to the second control signal transmitting through one optical fiber transmission path, the connection of the electric power feeding lines can be switched in the stable state of the electric power feeding lines. Therefore, there is no probability that a high voltage is generated in a connecting point of the electric power feeding lines so as to generate an electric arc, and a connection change of the electric power feeding lines can be reliably performed.
Also, in view of the fact that the electric power feeding line corresponding to the fault is earthed and because the electric power feeding lines corresponding to no fault are connected with each other, communication can be reliably performed through the optical fiber transmission paths corresponding to no fault.
It is also preferred that one electric power feeding line is earthed on a side of a connection point of the electric power feeding lines in an initial state, in which the feeding of the electric power to the other electric power feeding lines is started, by the electric power feeding line selector switch.
Because an electrostatic capacity of a system including the electric power feeding lines, the repeaters and the optical fiber transmission paths is reduced in the initial state, the feeding of electric power to the other electric power feeding lines can be easily started.
It is also preferred that the electric power feeding line switching apparatus further comprises:
monitoring means for monitoring an electric potential difference between an electric potential at a terminal of the electric power feeding line selector switch at which the electric power feeding lines are connected with each other and a ground level at another terminal of the electric power feeding line selector switch; and
monitor signal outputting means for producing an optical monitor signal indicating the electric potential difference monitored by the monitoring means and outputting the optical monitor signal to one of the optical fiber transmission paths.
In the above configuration, because the electric potential difference is monitored, the connection of the electric power feeding lines can be switched when it is detected according to the optical monitor signal that the electric potential difference is lowered. Therefore, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
It is also preferred that the electric power feeding line switching apparatus further comprises:
selector switch controlling means for transmitting the control signal detected by the control signal demultiplexing means to the electric power feeding line selector switch after an electric current supplied to a connection point of the electric power feeding lines is reduced to a minimum current required to switch the connection of the electric power feeding lines, wherein the connection of the electric power feeding lines is switched according to the control signal transmitted from the selector switch controlling means by the electric power feeding line selector switch after the electric current is reduced to the minimum current.
In the above configuration, because the connection of the electric power feeding lines is switched after the monitored electric potential difference is minimized, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
It is also preferred that the electric power feeding line selector switch has a for-opening-feeding-line selector switching element for making one end of one electric power feeding line open on a side of a connection point of the electric power feeding lines.
Because one electric power feeding line can be made open, the electric power feeding line switching apparatus can be applied to various connection types of electric power feeding lines.
The object is also achieved by the provision of an electric power feeding line switching system, in which a connection of a plurality of electric power feeding lines, each of which is connected with an optical fiber transmission path through a repeater to supply electric power from the electric power feeding lines to an optical communication signal of the optical fiber transmission paths through the repeaters, is switched, comprising:
a plurality of terminal stations, each of which is connected with one optical fiber transmission path and one electric power feeding line, for performing a communication operation by transmitting the optical communication signal through the optical fiber transmission paths, supplying the electric power to the electric power feeding lines, superposing a control signal on the optical communication signal and outputting the control signal superposed on the optical communication signal; and
an electric power feeding line switching apparatus for receiving the electric power from the terminal stations through the electric power feeding lines and switching from one connection of the electric power feeding lines to another connection of the electric power feeding lines according to the control signal transmitted from one of the terminal stations through one optical fiber transmission path.
In the above configuration, the switching of the connection of the electric power feeding lines is performed according to the control signal which is transmitted from one terminal station to the electric power feeding line switching apparatus through one optical fiber transmission path with the optical communication signal.
Accordingly, the connection of the electric power feeding lines can be switched according to the control signal when the electric power feeding lines are electrically set to a stable state, there is no probability that a high voltage is generated in a connecting point of the electric power feeding lines so as to generate an electric arc, and a connection change of the electric power feeding lines can be reliably performed.
Also, because the control signal transmits through one optical fiber transmission path, even though the optical fiber transmission path is long, electric power can be supplied from the electric power feeding line to the control signal of the optical fiber transmission path through the repeater connected with the optical fiber transmission path to amplify the control signal. Therefore, there is no probability that the control signal is attenuated, and the connection of the electric power feeding lines can be reliably switched according to the control signal regardless of the length of the optical fiber transmission path.
It is preferred that the electric power feeding line switching apparatus comprises
optical signal receiving means for receiving the optical communication signal which includes a control signal and transmits through the optical fiber transmission paths;
control signal demultiplexing means for detecting the control signal by demultiplexing the control signal from the optical communication signal received by the optical signal receiving means; and
an electric power feeding line selector switch for controlling the connection of the electric power feeding lines according to the control signal detected by the control signal demultiplexing means by switching one connection of the electric power feeding lines to another connection of the electric power feeding lines.
Because the connection of the electric power feeding lines can be switched according to the control signal when the electric power feeding lines are electrically set to a stable state, a connection change of the electric power feeding lines can be reliably performed.
Also, because the control signal transmits through one optical fiber transmission path, even though the optical fiber transmission path is long, the connection of the electric power feeding lines can be reliably switched according to the control signal regardless of the length of the optical fiber transmission path.
It is preferred that the electric power is supplied from one or more terminal stations connected with one or more electric power feeding lines corresponding to no fault in cases where a fault occurs in one of the electric power feeding lines, a second control signal is transmitted from one terminal station, which is connected with electric power feeding line corresponding to no fault, to the electric power feeding line switching apparatus through the optical fiber transmission path connected with the terminal station, one end of the electric power feeding line corresponding to the fault is earthed on a side of a connection point of the electric power feeding lines according to the second control signal by the electric power feeding line switching apparatus to disconnect the electric power feeding line corresponding to the fault from the electric power feeding lines corresponding to no fault, and the electric power feeding lines corresponding to no fault are connected with each other at the connection point according to the second control signal by the electric power feeding line switching apparatus to switch from the connection of all electric power feeding lines to another connection of the electric power feeding lines corresponding to no fault.
In the above configuration, even though a fault occurs in one electric power feeding line, because the connection switching of the electric power feeding lines is not performed according to a level change of the electric power feeding line but is performed according to the second control signal transmitting through one optical fiber transmission path, the connection of the electric power feeding lines can be switched in the stable state of the electric power feeding lines. Therefore, there is no probability that a high voltage is generated in a connecting point of the electric power feeding lines so as to generate an electric arc, and a connection change of the electric power feeding lines can be reliably performed.
Also, because the electric power feeding line corresponding to the fault is earthed and because the electric power feeding lines corresponding to no fault are connected with each other, communication can be reliably performed through the optical fiber transmission paths corresponding to no fault.
It is also preferred that one electric power feeding line is earthed on a side of a connection point of the electric power feeding lines in an initial state, in which the feeding of the electric power to the other electric power feeding lines is started, by the electric power feeding line switching apparatus.
Because an electrostatic capacity of a system including the electric power feeding lines, the repeaters and the optical fiber transmission paths is reduced in the initial state, the feeding of the electric power to the other electric power feeding lines can be easily started. It is also preferred that the electric power feeding line switching apparatus comprises:
monitoring means for monitoring an electric potential difference between an electric potential of a connection point of the electric power feeding lines connected with each other and a ground level; and
monitor signal outputting means for producing an optical monitor signal indicating the electric potential difference monitored by the monitoring means and outputting the optical monitor signal to one terminal station through one optical fiber transmission path connected with the terminal station, the connection of the electric power feeding lines is switched according to the control signal by the electric power feeding line switching apparatus while the terminal station monitoring the electric potential difference according to the optical monitor signal.
In the above configuration, because the electric potential difference is monitored, the connection of the electric power feeding lines can be switched when it is detected according to the optical monitor signal that the electric potential difference is lowered. Therefore, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
It is also preferred that the terminal station supplies a feeding current to the electric power feeding lines to maintain the feeding current supplied to the electric power feeding line switching apparatus while monitoring the electric potential difference according to the optical monitor signal, the terminal station controls the feeding current to minimize the electric potential difference, and the electric power feeding line switching apparatus switches the connection of the electric power feeding lines in cases where the electric potential difference is minimized.
In the above configuration, because the connection of the electric power feeding lines is switched when the monitored electric potential difference is minimized, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
It is also preferred that the electric power feeding line switching apparatus comprises:
selector switch controlling means for controlling the connection switching of the electric power feeding lines to switch the connection of the electric power feeding lines according to the control signal after an electric current supplied to a connection point of the electric power feeding lines is reduced by one terminal station to a minimum current required to switch the connection of the electric power feeding lines.
In the above configuration, because the connection of the electric power feeding lines is switched after the monitored electric potential difference is minimized, an electric stress such as an induced voltage occurring in the connection switching can be reduced, and the connection of the electric power feeding lines can be switched more stably.
It is also preferred that the electric power feeding line switching apparatus has a for-opening-feeding-line selector switching element for making one end of one electric power feeding line open on a side of a connection point of the electric power feeding lines.
Because one electric power feeding line can be made open, the electric power feeding line switching system can be applied to various connection types of electric power feeding lines.